2-mercapto-5-pyridyl-1,3,4-oxadiazoles and 2-mercapto-5-pyridyl-1,3,4-thiadiazoles of the formula I

ABSTRACT

The invention relates to 2-mercapto-5-pyridyl-1,3,4-oxadiazoles and 2-mercapto-5-pyridyl-1,3,4-thiadiazoles of the formula I ##STR1## wherein X is oxygen or sulfur, 
     R&#39; is C 1  -C 3  alkyl which is substituted by bromine, fluorine, C 1  -C 3  alkoxy or cyano; unsubstituted or halogen-substituted C 3  -C 7  alkenyl; unsubstituted or halogen-substituted C 4  -C 7  alkynyl, 
     R is C 1  -C 3  alkyl, unsubstituted C 1  -C 3  alkoxy or C 1  -C 3  alkoxy which is substituted by halogen or C 1  -C 3  alkoxy; unsubstituted or halogen-substituted C 3  -C 7  alkenyl; C 3  -C 7  alkynyl, C 1  -C 3  alkylthio, halogen, cyano, hydroxy, amino or amino which is substituted by one or two C 1  -C 3  alkyl groups; or is aminocarbonyl; and 
     n is 0, 1, 2, 3 or 4, 
     to the preparation of the compounds of formula I and to novel intermediates for the synthesis of these compounds. The compounds of formula I have nematicidal properties. The invention further relates to nematicidal compositions which contain at least one compound of formula I as active component, and to methods of using said compounds and of the compositions containing them for controlling nematodes.

The present invention relates to novel substituted2-mercapto-5-pyridyl-1,3,4-oxadiazoles and2-mercapto-5-pyridyl-1,3,4-thiadiazoles, to their preparation and tonematicidal compositions which contain at least one of these compoundsas active ingredient. The invention further relates to novelintermediates for the synthesis of the compounds of the invention and tothe use of 2-mercapto-5-pyridyl-1,3,4-oxadiazoles and2-mercapto-5-pyridyl-1,3,4-thiadiazoles and compositions containing themfor controlling nematicides, especially plant-destructive nematicides.

The 2-mercapto-5-pyridyl-1,3,4-oxadiazoles and2-mercapto-5-pyridyl-1,3,4-thiadiazoles of this invention, and saltsthereof, have the general formula I. ##STR2## wherein X is oxygen orsulfur,

R' is C₁ -C₃ alkyl which is substituted by bromine, fluorine, C₁ -C₃alkoxy or cyano; unsubstituted or halogen-substituted C₃ -C₇ alkenyl;unsubstituted or halogen-substituted C₄ -C₇ alkynyl,

R is C₁ -C₃ alkyl; or halo-C₁ -C₃ alkyl; unsubstituted C₁ -C₃ alkoxy orC₁ -C₃ alkoxy which is substituted by halogen or C₁ -C₃ alkoxy;unsubstituted or halogen substituted C₃ -C₇ alkenyl; C₃ -C₇ alkynyl, C₁-C₃ alkylthio, halogen, cyano, hydroxy, amino or amino which issubstituted by one or two C₁ -C₃ alkyl groups; or is aminocarbonyl; and

n is 0; 1; 2; 3 or 4.

Alkyl by itself or as moiety of another substituent such as alkoxy willbe understood as meaning straight chain and branched alkyl groups. Suchgroups include methyl, ethyl as well as the propyl and isopropyl group.Halogen-substituted alkyl is a mono- to perhalogented alkyl group, e.g.CHCl₂, CH₂ F, CCl₃, CH₂ Cl; CHFCH₃, CH₂ CH₂ Br, CF₂ CF₃, C₂ Cl₅, CH₂ Br,CHBrCl and the like, and is preferably CHF₂. Alkenyl is typically1-propenyl, allyl, 1-butenyl, 2-butenyl or 3-butenyl, as well as chainscontaining several double bonds. Alkynyl is typically 2-propynyl,1-butynyl, 2-butynyl, 4-pentynyl and the like. Halogen is fluorine,chlorine, bromine or iodine, and is preferably fluorine, chlorine orbromine.

Examples of salt-forming inorganic acids are hydrohalic acids such ashydrofluoric acid, hydrochloric acid, hydrobromic acid or hydriodicacid, as well as sulfuric acid, phosphoric acid, phosphorous acid andnitric acid; examples of salt-forming organic acids are acetic acid,trifluoroacetic acid, trichloroacetic acid, propionic acid, glycolicacid, thiocyanic acid, lactic acid, succinic acid, citric acid, benzoicacid, cinnamic acid, oxalic acid, formic acid, benzenesulfonic acid,p-toluenesulfonic acid, methanesulfonic acid, salicylic acid,p-aminosalicylic acid, 2-phenoxybenzoic acid and 2-acetoxybenzoic acid.

Oxadiazole and thiadiazole derivatives disclosed as having nematicidalproperties are known. Thus U.S. Pat. No. 3,770,754 discloses suchcompounds with hetero atoms in 1,2,4-position, whereas U.S. Pat. No.4,454,147 describes 1,3,4-thiadiazole derivatives in which, as comparedwith the compounds of this invention, the heterocycle is substituted bya chlorine atom instead of by mercapto groups. As nematicides theseknown compounds have so far been unable to meet fully the demands madeof them in practice. Further, oxadiazole derivatives having fungicidalproperties are disclosed in German Offenlegungsschrift 2 361 613.However, this reference does not expressly mention any of thesecompounds that fall within the scope of formula I of the presentinvention.

With the compounds of formula I of the present invention it is nowpossible to make a valuable contribution to controlling plant nematodeswhich cause considerable agricultural damage to plants. By controllingsuch nematodes, harvest losses of cultivated plants such as potatoes,cereals, carrots, rape, cabbage and vegetables and also damage caused innurseries and to ornamentals can be inhibited in the long term. Thecompounds of the present invention are distinguished in particular bythe feature that they effectively control soil nematodes whichparasitise on roots, e.g. those nematodes of the genera Heterodera andGlobodera (cystogenic nematodes), Meloidogyne (root-knot nematodes) andalso of the genera Radopholus, Pratylenchus, Longidorus, Trichodorus,and Xiphinema. The nematode genera Ditylenchus (stem parasites),Aphelenchoides (bud and leaf nematodes) and Anguina (seed-gallnematodes) can also be effectively controlled with the compounds of thisinvention.

Preferably the compounds of formula I are used for effectivelycontrolling particularly harmful nematode species of the genusMeloidogyne, e.g. Meloidogyne incognita, of the genus Heterodera, e.g.Heterodera glycines (soybean cyst nematode), of the genus Globodera,e.g. Globodera rostochienis (potato cyst nematode), as well asrepresentatives of migrating endoparasites such as Pratylenchuspenetrans or Radopholus similis, and representatives of ectoparasitessuch as Trichodorus spp. and Xiphinema spp.

To control plant nematodes and for the preservation of plant health, thenovel compounds may be used curatively, preventively or systemically.They have a wide activity spectrum against the various nematode speciesand therefore meet the requirements made of them in practice. Thenematicidal mode of action of the compounds of the present invention isadvantageously coupled with their low phytotoxicity, whereby thegenerally desirable lessening of risk to the environment is especiallytaken into account.

Within the scope of this invention, the following groups of compoundsand individual compounds of formula I are preferred:

1. Those 2-mercapto-5-(pyid-2-yl)-1,3,4-oxadiazoles of formula Ia##STR3## wherein R' is difluoromethyl, R₁, R₂ and R₃ are hydrogen and R₄is aminocarbonyl or hydroxy; and also those wherein R' isdifluoromethyl, cyanomethyl or propargyl, and R₁, R₂, R₃ and R₄ arehydrogen.

1.1 Among these compounds,2-difluoromethylthio-5-(pyrid-2-yl)-1,3,4-oxadizaole is particularlypreferred.

2. Those 2-mercapto-5-(pyid-2-yl)-1,3,4-thiadiazoles of formula Ib##STR4## wherein R' is C₁ -C₃ alkyl which is substituted by bromine,fluorine or cyano; allyl or halogen-substituted allyl; R₁, R₂, R₃ and R₄are each independently hydrogen, methyl, difluoromethyl,trifluoromethyl, methoxy, methylmercapto, chlorine, cyano, hydroxy,amino or aminocarbonyl.

Among these compounds, those compounds are particularly preferred inwhich

2.1 R₁ and R₄ are each independently of the other hydrogen or chlorine,and R₂ and R₃ are hydrogen; and also those in which

2.2 R' is difluoromethyl, R₁, R₂ and R₃ are hydrogen and R₄ is methyl,trifluoromethyl, methoxy, chlorine, cyano, aminocarbonyl, hydroxy oramino; as well as those in which

2.3 R' is difluoromethyl, one of the substituents R₁, R₂ and R₃ ismethyl, chlorine, methoxy or methylmercapto and the other twosubstituents are hydrogen and R₄ is hydrogen; and, finally those inwhich

2.4 R' is difluoromethyl, R₁ and R₄ are each independently of the otherhydrogen, chlorine, methoxy or hydroxy, and R₂ and R₃ are hydrogen.

2.4.1. Among this last mentioned group of compounds,2-difluoromethyltio-5-(pyrid-2-yl)-1,3,4-thiadiazole is particularlypreferred.

3.1 Those 2-mercapto-5-(pyrid-2-yl)-1,3,4-oxadiazoles of formula Ic##STR5## wherein R' is difluoromethyl and one of the substituents R₁,R₂, R₃ and R₄ is methyl, methylmercapto or halogen and the others arehydrogen; and those wherein

3.2 R' is difluoromethyl and two of the substituents R₁ to R₄ are eachindependently of the other methyl or chlorine and R₂ and R₃ arehydrogen; as well as those wherein

3.3 R' is difluoromethyl, R₁ and R₄ are chlorine and one of thesubstituents R₂ and R₃ is hydrogen or chlorine; and finally,

3.4 difluoromethylthio-5-(pyrid-2-yl)-1,3,4-oxadiazole.

4.1 Those 2-mercapto-5-(pyrid-3-yl)-thiadiazoles of formula Id ##STR6##wherein R' is difluoromethyl or difluoromethyldifluoromethyl and R₁, R₂,R₃ and R₄ are hydrogen; and also those wherein

4.2 R' is difluoromethyl, R₁ is hydrogen, C₁ -C₃ alkyl or chlorine, R₂is hydrogen and R₃ and R₄ are each independently of the other hydrogenor chlorine or methoxy; and finally, those wherein

4.3 R' is difluoromethyl, R₁, R₂ and R₄ are each independently hydrogen,chlorine, bromine, methylthio or amino, and R₃ is hydrogen.

4.3.1 Among this last mentioned group,2-difluoromethylthio-5-(pyrid-3-yl)-1,3,4-thiadiazole is particularlypreferred.

5. Those 2-mercapto-5-(pyrid-4-yl)-oxadiazoles of formula Ie ##STR7##wherein R' is difluoromethyl, difluoromethyldifluoromethyl orcyanomethyl, and R₁, R₂, R₃ and R₄ are hydrogen.

6. Those 2-mercapto-5-(pyrid-4-yl)-thiadiazoles of formula If ##STR8##wherein R₂ and R₃ are hydrogen.

6.1 Among these compounds, those compounds are particularly preferred inwhich R' is difluoromethyl, difluoromethyldifluoromethyl, cyanomethyl or2-bromoallyl, R₁ is hydrogen, C₁ -C₄ alkyl, chlorine, methoxy ormethylmercapto, R₄ is hydrogen, methyl, chlorine, methoxyethoxy,trifluoromethylmethoxy, methylmercapto, amino or C₁ -C₃ monoalkylamino.

6.2 Among this last mentioned group of compounds,2-difluoromethylthio-5-(pyrid-4-yl)-1,3,4-thiadiazole is particularlypreferred.

The compounds of formula I are prepared by

(a) condensing a compound of formula II ##STR9## or a compound offormula III ##STR10## with a compound of formula IV

    Hal--R'                                                    (IV)

in an inert solvent or mixture of solvents at room temperature or atelevated temperature, in the absence or presence of a catalyst and undernormal or elevated pressure, the reaction being carried out in thepresence of a base if the starting material is a compound of formula II;or

(b) reacting a compound of formula II ##STR11## with a compound offormula V ##STR12## in an inert solvent or mixture of solvents atelevated temperature and in the absence or presence of a catalyst andunder normal or elevated pressure, by means of an addition reaction togive a compound of formula Ig ##STR13## or a compound of formula Ih##STR14## in which formulae II, III, IV, V, Ig and Ih above Me is analkali metal or ammonium, Hal is halogen, preferably chlorine, bromineor iodine, and R" is fluorine or trifluoromethyl, and R, R' and n aredefined for formula I.

Examples of solvents or diluents suitable for the preparation of thecompounds of this invention are ethers and etheral compounds such asdialkyl ethers (diethyl ether, diisopropyl ether, tert-butylmethyl etherand the like), anisole, dioxane, tetrahydrofuran; aliphatic and aromatichydrocarbons such as benzene, toluene, petroleum ether; halogenatedhydrocarbons such as chlorobenzene, mehylene chloride, chloroform,ethylene chloride, carbon tetrachloirde, tetrachloroethylene; nitrilessuch as acetonitrile, propionitrile; N,N-dialkylated amides such asdimethylformamide; dimethyl sulfoxide; ketones such as acetone, diethylketone, methyl ethyl ketone; and also water and alcohols such asmethanol, ethanol, isopropanol or butanol; and, quite generally,mixtures of such solvents with one another.

Suitable bases are both organic and inorganic bases; e.g. preferablytertiary amines such as trialkylamines (trimethylamine, triethylamine,tripropylamine and others), as well as oxides, hydroxides, carbonatesand bicarbonates of alkali metals and alkaline earth metals (e.g. CaO,BaO, NaOH, KOH, Ca(OH)₂, KHCO₃, NaHCO₃, Ca(HCO₃)₂, K₂ CO₃, Na₂ CO₃etc.), and also acetates such as CH₃ COONa or CH₃ COOK. Further suitablebases are alkali metal alcoholates such as sodium methylate, sodiumpropylate, potassium tert-butylate or sodium ethylate.

The addition of catalytic amounts of a crown ether, e.g. 18-crown-6 or15-crown-5 promotes the reaction course of the preparatory processes.The catalytic addition of tetraalkylamine salts, e.g. tetraalkylaminochlorides or bromides, preferably tetra-n-butylamino bromide, is alsouseful for the same purpose. In addition, alkali metal iodides,preferably potassium iodide, may be used with advantage as catalysts.

The reaction temperatures in the preparatory processes are in the rangefrom 10° to 90° C., preferably from 30° to 80° C. The reaction has to becarried out under atmospheric or under elevated pressure.

Some of the starting compounds of formula II are known and some arenovel. Novel compounds are those2-mercapto-5-pyrid-2-yl-1,3,4-oxadiazole of formula IIa' ##STR15##2-mercapto-5-pyrid-2-yl-1,3,4-thiadiazoles of formula IIb' ##STR16##2-mercapto-5-pyrid-3-yl-1,3,4-oxadiazoles of formula IIc' ##STR17##2-mercapto-5-pyrid-3-yl-1,3,4-thiadiazoles of formula IId' ##STR18##2-mercapto-5-pyrid-4-yl-1,3,4-oxadiazoles of formula IIe' ##STR19## and2-mercapto-5-pyrid-4-yl-1,3,4-thiadiazoles of formula IIf' ##STR20##wherein R₁, R₂, R₃ and R₄ are each independently methyl, propyl orisopropyl, unsubstituted C₁ -C₃ alkoxy or C₁ -C₃ alkoxy which issubstituted by halogen or C₁ -C₃ alkoxy, unsubstituted orhalogen-substituted C₃ -C₇ alkenyl; or are C₄ -C₇ alkynyl, C₁ -C₃alkylthio, halogen, cyano, hydroxy, amino or amino which is substitutedby one or two C₁ -C₃ alkyl groups; or are aminocarbonyl.

The novel compounds of formulae IIa' to IIf' (q.v. Table 0) areintermediates for the preparation of useful nematicides and thusconstitute an object of the present invention.

The starting compounds of formula II can be prepared by known methods[Salama et al: Egypt J. Chem. 1981 (Pub. 1982) 24 (1-3) 47-51 CA. 99,53674 y (1983): Pol. J. Pharmacol. Pharm. 1981, 33(5), 527-32, CA. 97,6229 f, 1982; Chem. Pharm. Bull. 1970, 18(8), 1696-8, CA. 73, 98877 w,1970] or by methods analogous thereto.

The compounds of formulae IV and V are known, commercially availableproducts.

The invention also relates to compositions for controllingplantdestructive nematodes and also for protecting plants from attack bynematodes, which compositions contain compounds of formula I.

The present invention also relates to the preparation of nematicidalcompositions, which comprises homogeneously mixing compounds of formulaI with one or more of the carriers and adjuvants described herein. Theinvention further relates to a method of treating plants, whichcomprises applying thereto the compounds of formula I" ##STR21## whereinX is oxygen or sulfur,

R is hydrogen, C₁ -C₃ alkyl, C₁ -C₃ alkoxy which is substituted byhalogen or C₁ -C₃ alkoxy; C₃ -C₇ alkenyl or halogen-substituted C₃ -C₇alkenyl; C₃ -C₇ alkynyl, C₁ -C₃ alkylthio, cyano, hydroxy, amino oramino which is substituted by one or two C₁ -C₃ alkyl groups; or isaminocarbonyl,

R' is C₁ -C₃ alkyl which is substituted by halogen, C₁ -C₃ alkoxy orcyano; C₃ -C₇ alkenyl or halogen-substituted C₃ -C₇ alkenyl;unsubstituted or halogen-substituted C₃ -C₇ alkynyl; and

n is 0, 1, 2, 3 or 4,

or the novel compositions.

A preferred method of applying a compound of formula I or I" or anematicidal composition containing at least one of these compounds issoil application, which comprises treating the locus of the plants witha liquid or solid formulation.

The compounds of formula I" may also be applied to seeds(dressing/coating) either by impregnating the seeds in a liquidformulation of the active ingredient or by coating them with a solidformulation. Moreover, in special cases, further types of applicationare also possible, e.g. selective treatment of the plant stems, buds orleaves.

The compounds of formula I" are normally applied in the form ofcompositions and can be applied to the crop area or plant to be treated,simultaneously or in succession, with further compounds. These furthercompounds can also include other substances applied in agriculture whichare used to increase production by promoting the growth of usefulplants. Examples of such substances are fertilisers, herbicides,insecticides, fungicides, mollusicides and the like, or mixtures ofseveral of these substances, if desired, together with further carriers,surfactants or other application promoting adjuvants customarilyemployed in the art of formulation.

Suitable carriers and adjuvants can be solid or liquid and correspond tothe substances ordinarily employed in formulation technology, e.g.natural or regenerated mineral substances, solvents, dispersants,wetting agents, tackifiers, thickeners, binders or fertilisers.

The compounds of formula I" are used in unmodified form or, preferably,together with the adjuvants conventionally employed in the art offormulation, and are therefore formulated in known manner toemulsifiable concentrates, directly sprayable or dilutable solutions,dilute emulsions, wettable powders, soluble powders, dusts, granulates,and also encapsulations in e.g. polymer substances. As with the natureof the compositions, the methods of application, such as spraying,dusting, scattering or pouring, are chosen in accordance with theintended objectives and the prevailing circumstances. Advantageous ratesof application are normally from 500 g to 6 kg of active ingredient(a.i.) per hectare, preferably from 1 to 4 kg a.i./ha.

The formulations, i.e. the compositions containing the compound (activeingredient) of formula I" and, where appropriate, a solid or liquidadjuvant, are prepared in known manner, e.g. by homogeneously mixingand/or grinding the active ingredients with extenders, e.g. solvents,solid carriers and, where appropriate, surface-active compounds(surfactants).

Suitable solvents are: aromatic hydrocarbons, preferably the fractionscontaining 8 to 12 carbon atoms, e.g. xylene mixtures or substitutednaphthalenes, phthalates such as dibutyl phthalate or dioctyl phthalate,aliphatic hyrdocarbons such as cyclohexane or paraffins, alcohols andglycols and their ethers and esters, such as ethanol, ethylene glycol,ethylene glycol monomethyl or monoethyl ether, ketones such ascyclohexanone, strongly polar solvents such as N-methyl-2-pyrrolidone,dimethyl sulfoxide or dimethylformamide, as well as vegetable oils orepoxidised vegetable oils such as epoxidised coconut oil, sunflower oilor soybean oil; or water.

The solid carriers used e.g. for dusts and dispersible powders, arenormally natural mineral fillers such as calcite, talcum, kaolin,montmorillonite or attapulgite. In order to improve the physicalproperties it is also possible to add highly dispersed silicic acid orhighly dispersed absorbent polymers. Suitable granulated adsorptivecarriers are porous types, for example pumice, broken brick, sepioliteor bentonite; and suitable nonsorbent carriers are materials such ascalcite or sand. In addition, a great number of pregranulated materialsof inorganic or organic nature can be used, e.g. especially dolomite orpulverised plant residues.

Depending on the nature of the compound of formula I" to be formulated,suitable surface-active compounds are non-ionic, cationic and/or anionicsurfactants having good emulsifying, dispersing and wetting properties.The term "surfactants" will also be understood as comprising mixtures ofsurfactants.

Suitable anionic surfactants can be both water-soluble soaps andwater-soluble synthetic surface-active compounds.

Suitable soaps are the alkali metal salts, alkaline earth metal salts orunsubstituted or substituted ammonium salts of higher fatty acids (C₁₀-C₂₂), e.g. the sodium or potassium of oleic or stearic acid, or ofnatural fatty acid mixtures which can be obtained e.g. from coconut oilor tallow oil. Mention may also be made of fatty acid methyltaurinsalts.

More frequently, however, so-called synthetic surfactants are used,especially fatty sulfonates, fatty sulfates, sulfonated benzimidazolederivatives or alkylsulfonates.

The fatty sulfonates or sulfates are usually in the form of alkali metalsalts, alkaline earth metal salts or unsubstituted or substitutedammonium salts and contain a C₈ -C₂₂ alkyl radical which also includesthe alkyl moiety of acyl radicals, e.g. the sodium or calcium salt oflignosulfonic acid, of dodecylsulfate or of a mixture of fatty alcoholsulfates obtained from natural fatty acids. These compounds alsocomprise the salts of sulfuric acid esters and sulfonic acids of fattyalcohol/ethylene oxide adducts. The sulfonated benzimidazole derivativespreferably contain 2 sulfonic acid groups and one fatty acid radicalcontaining 8 to 22 carbon atoms. Examples of alkylarylsulfonates are thesodium, calcium or triethanolamine salts of dodecylbenzenesulfonic acid,dibutylnaphthalenesulfonic acid, or of a naphthalenesulfonicacid/formaldehyde condensation product. Also suitable are correspondingphosphates, e.g. salts of the phosphoric acid ester of an adduct ofp-nonylphenol with 4 to 14 moles of ethylene oxide.

Non-ionic surfactants are preferably polyglycol ether derivatives ofaliphatic or cycloalaiphatic alcohols, or saturated or unsaturated fattyacids and alkylphenols, said derivatives containing 3 to 30 glycol ethergroups and 8 to 20 carbon atoms in the (aliphatic) hydrocarbon moietyand 6 to 18 carbon atoms in the alkyl moiety of the alkylphenols.

Further suitable non-ionic surfactants are the water-soluble adducts ofpolyethylene oxide with polypropylene glycol, ethylenediamino-propyleneglycol and alkylpolypropylene glycol containing 1 to 10 carbon atoms inthe alkyl chain, which adducts contact 20 to 250 ethylene glycol ethergroups and 10 to 100 propylene glycol ether groups. These compoundsusually contain 1 to 5 ethylene glycol units per propylene glycol unit.

Representative examples of non-ionic surfactants arenonylphenolpolyethoxyethanols, castor oil polyglycol ethers,polypropylene/polyethylene oxide adducts,tributylphenoxypolyethyleneethanol, polyethylene glycol andoctylphenoxypolyethoxyethanol. Fatty acid esters of polyoxyethylenesorbitan, e.g. polyoxyethylene sorbitan trioleate, are also suitablenon-ionic surfactants.

Cationic surfactants are preferably quaternary ammonium salts whichcontain, as N-substituent, at least one C₈ -C₂₂ alkyl radical and, asfurther substituents, unsubstituted or halogenated alkyl, benzyl orhydroxy-lower alkyl radicals. The salts are preferably in the form ofhalides, methylsulfates or ethylsulfates, e.g. stearyltrimethylammoniumchloride or benzyldi(2-chloroethyl)ethylammonium bromide.

The surfactants customarily employed in the art of formulation aredescribed e.g. in "McCutcheon's Detergents and Emulsifiers Annual", MCPublishing Corp., Ridgewood, N.J., 1979; Dr. Helmut Stache, "TensidTaschenbuch" (Handbook of Surfactants), Carl Hanser Verlag,Munich/Vienna, 1981.

The agrochemical compositions usually contain 0.1 to 99% by weight,preferably 0.1 to 95% by weight, of a compound of formula I, 99.9 to 1%by weight, preferably 99.8 to 5% by weight, of a solid or liquidadjuvant, and 0 to 25% by weight, preferably 0.1 to 25% by weight, of asurfactant.

Whereas commercial products will preferably be formulated asconcentrates, the end user will normally employ dilute formulations.

The compositions may also contain further auxiliaries such asstabilisers, antifoams, viscosity regulators, binders, tackifiers aswell as fertilisers or other active ingredients for obtaining specialeffects.

Such agrochemical compositions constitute an object of the presentinvention.

The invention is illustrated in more detail by the followingnonlimitative Examples.

l. Preparatory Examples Example 0.42-Mercapto-5-(pyrid-3-yl)-1,3,4-oxadiazole ##STR22##

13.7 g (0.1 mol) of nicotinic acid hydrazide and 8 g (0.105 mol) ofcarbon disulfide are added dropwise to a solution of 56 g (0.1 mol) ofpotassium hydroxide in 20 g of water and 350 ml of 95% ethanol. Thereaction mixture is refluxed for 3 hours, then the solvent is evaporatedoff under vacuum and the residue is dried under a high vacuum. The dryresidue is stirred in 75 ml of water, filtered, and the filtrate isneutralised with 1N hydrochloric acid. The precipitated product isisolated by filtration, washed in succession with acetone and hexane andvacuum dried, affording 9.9 g (55% of theory) of the title compound witha melting point of 237° C.

Example 1.1 2-Difluoromethylthio-5-pyrid-2-yl-1,3,4-thiadiazole##STR23##

A suspension of 341.5 g (l.75 mol) of2-mercapto-5-pyrid-2-yl-1,3,4-thiadiazole in 4000 ml of dioxane is addedto a solution of 230.5 g of 85% potassium hydroxide in 800 ml of water.Then 10 g of potassium iodide and 6 g of tributylammonium bromide areadded to the reaction mixture and 750 g (˜8.6 mol) of gaseousdifluoromethane are introduced over 41/2 hours at 22°-37° C. Afterevaporating off the dioxane, the reaction mixture is diluted with ethylacetate, the aqueous phase is separated and the organic solution iswashed cold with 1N sodium hydroxide and water, dried over sodiumsulfate and clarified with activated carbon. They ethyl acetate isremoved under vacuum and the residue is crystallised from ethylacetate/hexane, affording 321.9 g (75.1%) of the title compound with amelting point of 90°-92° C.

The following compounds of this invention can be prepared in accordancewith the foregoing Preparatory Examples and with the processes describedabove. These compounds serve to illustrate the invention and imply nolimitation thereof.

                  TABLE 0                                                         ______________________________________                                         ##STR24##                                                                    Compound                                                                              Q               X       Phys. data                                    ______________________________________                                        0.1                                                                                    ##STR25##      S       m.p. >200° C.                          0.2                                                                                    ##STR26##      O       m.p. >200° C.                          0.3                                                                                    ##STR27##      S       m.p. 276-279° C.                       0.4                                                                                    ##STR28##      O       m.p. 237° C.                           0.5                                                                                    ##STR29##      S       m.p. >200°  C.                         0.6                                                                                    ##STR30##      O       m.p. >200° C.                          0.7                                                                                    ##STR31##      S       m.p. 192-194° C.                       0.8                                                                                    ##STR32##      O       m.p. 202-205° C.                       0.9                                                                                    ##STR33##      S       m.p. 215-218° C.                       0.10                                                                                   ##STR34##      S       m.p. 153-156° C.                       0.11                                                                                   ##STR35##      S                                                     0.12                                                                                   ##STR36##      S                                                     0.13                                                                                   ##STR37##      S                                                     0.14                                                                                   ##STR38##      S                                                     0.15                                                                                   ##STR39##      S                                                     0.16                                                                                   ##STR40##      S                                                     0.17                                                                                   ##STR41##      S                                                     0.18                                                                                   ##STR42##      S                                                     0.19                                                                                   ##STR43##      S                                                     0.20                                                                                   ##STR44##      S                                                     0.21                                                                                   ##STR45##      S                                                     0.22                                                                                   ##STR46##      S                                                     0.23                                                                                   ##STR47##      S       m.p. >200° C.                          0.24                                                                                   ##STR48##      S                                                     0.25                                                                                   ##STR49##      S       m.p. >200° C.                          0.26                                                                                   ##STR50##      S                                                     0.27                                                                                   ##STR51##      O       m.p. >200° C.                          0.28                                                                                   ##STR52##      O       m.p. >200° C.                          0.29                                                                                   ##STR53##      O       m.p. >200° C.                          0.30                                                                                   ##STR54##      S       m.p. >250° C.                          0.31                                                                                   ##STR55##      O       m.p. >250° C.                          ______________________________________                                    

                                      TABLE 1                                     __________________________________________________________________________     ##STR56##                                                                    Com-                                   Physical                               pound                                                                             R'         R.sub.1                                                                            R.sub.2                                                                           R.sub.3                                                                            R.sub.4                                                                             X   data                                   __________________________________________________________________________    1.1 CHF.sub.2  H    H   H    H     S   m.p. 90-92° C.                  1.2 CHF.sub.2  H    H   H    H     O   m.p. 82-84° C.                  1.3 CHF.sub.2  CH.sub.3                                                                           H   H    H     S                                          1.4 CHF.sub.2  H    CH.sub.3                                                                          H    H     S                                          1.5 CHF.sub.2  H    H   CH.sub.3                                                                           H     S                                          1.6 CHF.sub. 2 H    H   H    CH.sub.3                                                                            S                                          1.7 CHF.sub.2  Cl   H   H    H     S                                          1.8 CHF.sub.2  H    H   H    Cl    S                                          1.9 CHF.sub.2  H    H   H    CN    S                                          1.10                                                                              CHF.sub.2  H    H   H    CONH.sub.2                                                                          S                                          1.11                                                                              CHF.sub.2  H    H   H    CONH.sub.2                                                                          O                                          1.12                                                                              CHF.sub.2  H    H   OCH.sub.3                                                                          H     S                                          1.13                                                                              CHF.sub.2  CH.sub.3 O                                                                         H   H    H     S                                          1.14                                                                              CHF.sub.2  H    H   H    CF.sub.3                                                                            S                                          1.15                                                                              CHF.sub.2  H    Cl  H    H     S                                          1.16                                                                              CHF.sub.2  H    H   Cl   H     S                                          1.17                                                                              CH.sub.2 CCH                                                                             H    H   H    H     S   m.p. 87-87°  C.                 1.18                                                                              CH.sub.2 CCH                                                                             H    H   H    H     O                                          1.19                                                                              CH.sub.2 CCH                                                                             H    H   H    Cl    S                                          1.20                                                                              CH.sub.2 CHCH.sub.2                                                                      H    H   H    H     S                                          1.21                                                                               ##STR57## H    H   H    H     S   m.p. 87-88° C.                  1.22                                                                              C.sub.3 H.sub.7 (i)                                                                      H    H   H    H     S                                          1.23                                                                              CF.sub.2 CHF.sub.2                                                                       H    H   H    H     S                                          1.24                                                                              CF.sub.2 CHF.sub.2                                                                       Cl   H   H    H     S                                          1.25                                                                              CHF.sub.2  Cl   H   H    Cl    S                                          1.26                                                                              CHF.sub.2  Cl   H   H    Cl    O                                          1.27                                                                              CHF.sub.2  Cl   H   H    OCH.sub.3                                                                           S                                          1.28                                                                              CHF.sub.2  Cl   H   H    OH    S                                          1.29                                                                              CHF.sub.2  H    H   H    OH    S                                          1.30                                                                              CHF.sub.2  H    H   H    OH    O                                          1.31                                                                              CHF.sub.2  H    H   H    OCH.sub.3                                                                           S                                          1.32                                                                              CHF.sub.2  H    H   H    NH.sub.2                                                                            S                                          1.33                                                                              CHF.sub.2  CH.sub.3 S                                                                         H   H    H     S                                          1.34                                                                              CH.sub.2 CN                                                                              H    H   H    H     S                                          1.35                                                                              CH.sub.2 CN                                                                              H    H   H    H     O                                          1.36                                                                              CBrF.sub.2 H    H   H    H     S                                          1.37                                                                              CBrF.sub.2 H    H   H    H     O                                          1.38                                                                              CH.sub.2 CH.sub.2 CFCF.sub.2                                                             H    H   H    H     S   m.p. 63-66° C.                  1.39                                                                              CH.sub.2 CH.sub.2 CFCF.sub.2                                                             H    H   H    H     O   m.p. 44-45° C.                  1.40                                                                              CH.sub.2 CH.sub.2 CFCF.sub.2                                                             H    H   H    J     O                                          1.41                                                                              CH.sub.2 CH.sub.2 CFCF.sub.2                                                             H    H   H    J     S                                          1.42                                                                              CHF.sub.2  H    H   H    J     O                                          1.43                                                                              CHF.sub.2  H    H   H    J     S                                          __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________     ##STR58##                                                                    Com-                                  Physical                                pound                                                                             R'         R.sub.1                                                                             R.sub.2                                                                          R.sub.3                                                                            R.sub.4                                                                            X   data                                    __________________________________________________________________________    2.1 CHF.sub.2  H     H  H    H    S   m.p. 86° C.                      2.2 CHF.sub.2  H     H  H    H    O   n.sub.D.sup.20 : 1.5715                 2.3 CHF.sub.2  CH.sub.3                                                                            H  H    Cl   S                                           2.4 CHF.sub.2  CH.sub.3                                                                            H  H    Cl   O                                           2.4 CHF.sub.2  Cl    H  Cl   H    S                                           2.6 CHF.sub.2  Cl    H  Cl   H    O                                           2.7 CHF.sub.2  H     H  OCH.sub.3                                                                          OCH.sub.3                                                                          S                                           2.8 CHF.sub.2  CH.sub.3                                                                            H  Cl   Cl   S                                           2.9 CHF.sub.2  CH.sub.3                                                                            H  Cl   Cl   O                                           2.10                                                                              CH.sub.2 CH                                                                              H     H  H    H    S   wax                                     2.11                                                                              CF.sub.2 CHF.sub.2                                                                       H     H  H    H    S   m.p. 95-98° C.                   2.12                                                                              CHF.sub.2  Cl    H  H    Cl   S                                           2.13                                                                              CHF.sub.2  Cl    H  H    Cl   O                                           2.14                                                                              CHF.sub.2  C.sub.3 H.sub.7 (n)                                                                 H  H    Cl   S                                           2.15                                                                              CHF.sub.2  Cl    Cl H    Cl   S                                           2.16                                                                              CHF.sub.2  Cl    Cl H    Cl   O                                           2.17                                                                              CHF.sub.2  H     Br H    NH.sub.2                                                                           S                                           2.18                                                                              CHF.sub.2  H     H  H    NH.sub.2                                                                           S                                           2.19                                                                              CHF.sub.2  H     Br H    H    S   m.p. 125-127° C.                 2.20                                                                              CHF.sub.2  H     Br H    H    O   m.p. 100-101° C.                 2.21                                                                              CHF.sub.2  Cl    H  H    H    S                                           2.22                                                                              CHF.sub.2  Cl    H  H    H    O                                           2.23                                                                              CHF.sub.2  H     H  H    SCH.sub.3                                                                          S   m.p. 69-71° C.                   2.24                                                                              CHF.sub.2  H     H  H    SCH.sub.3                                                                          O   m.p. 58-60° C.                   2.25                                                                              CH.sub.3   H     H  H    H    O   m.p. 59-64° C.                   2.26                                                                              C.sub.2 H.sub.5                                                                          H     H  H    H    O   m.p. 67-69° C.                   2.27                                                                              CH(CH.sub.3).sub.2                                                                       H     H  H    H    O   n.sub.D.sup.20 : 1.5830                 2.28                                                                              CH.sub.2CH CH.sub.2                                                                      H     H  H    H    O   m.p. 62-64° C.                   2.29                                                                              CH.sub.2 CCH                                                                             H     H  H    H    O   m.p. 68-71° C.                   2.30                                                                              CH.sub.2 CN                                                                              H     H  H    H    O   m.p. 123-125° C.                 2.31                                                                              CH.sub.2 CN                                                                              H     H  H    H    S                                           2.32                                                                              CBrF.sub.2 H     H  H    H    S                                           2.33                                                                              CBrF.sub.2 H     H  H    H    O                                           2.34                                                                              CHF.sub.2  CH.sub.3                                                                            H  H    H    S                                           2.35                                                                              CHF.sub.2  CH.sub.3                                                                            H  H    H    O                                           2.36                                                                              CH.sub.2 CH.sub.2 CFCF.sub.2                                                             CH.sub.3                                                                            H  H    H    O                                           2.37                                                                              CH.sub.2 CH.sub.2 CFCF.sub.2                                                             CH.sub.3                                                                            H  H    H    S                                           2.38                                                                              CH.sub.2 CH.sub.2 CFCF.sub.2                                                             H     H  H    H    O                                           2.39                                                                              CH.sub.2 CH.sub.2 CFCF.sub.2                                                             H     H  H    H    S                                           2.40                                                                              CHF.sub.2  CF.sub.3                                                                            H  H    H    O                                           2.41                                                                              CHF.sub.2  CF.sub.3                                                                            H  H    H    S                                           2.42                                                                              CH.sub.2 CH.sub.2 CFCF.sub.2                                                             CF.sub.3                                                                            H  H    H    O                                           2.43                                                                              CH.sub.2 CH.sub.2 CFCF.sub.2                                                             CF.sub.3                                                                            H  H    H    S                                           __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________     ##STR59##                                                                    Com-                                     Physical                             pound                                                                             R'         R.sub.1                                                                             R.sub.2                                                                          R.sub.3                                                                          R.sub.4   X   data                                 __________________________________________________________________________    3.1 CHF.sub.2  H     H  H  H         S   m.p. 87-90° C.                3.2 CHF.sub.2  Cl    H  H  Cl        S   m.p. 59-62° C.                3.3 CHF.sub.2  Cl    H  H  Cl        O                                        3.4 CHF.sub.2  CH.sub.3                                                                            H  H  Cl        S                                        3.5 CHF.sub.2  Cl    H  H  H         S                                        3.6 CHF.sub.2  OCH.sub.3                                                                           H  H  H         S                                        3.7 CHF.sub.2  CH.sub.3                                                                            H  H  H         S                                        3.8 CHF.sub.2  OCH.sub.3                                                                           H  H  Cl        S   m.p. 82-85° C.                3.9 CHF.sub.2  Cl    H  H  OCH.sub.2 CH.sub.2 OCH.sub.3                                                            S   m.p. 76-79° C.                3.10                                                                              CH.sub.2 CCH                                                                             Cl    H  H  Cl        S   m.p. 134-137° C.              3.11                                                                              CH.sub.2 CCH                                                                             H     H  H  H         S                                        3.12                                                                              CH.sub.2 CCH                                                                             OCH.sub.3                                                                           H  H  Cl        S   m.p. 131-133° C.              3.13                                                                              CH.sub.2 CCH                                                                             Cl    H  H  OCH.sub.2 CH.sub.2 OCH.sub.3                                                            S   m.p. 119-121° C.              3.14                                                                               ##STR60## H     H  H  H         S                                        3.15                                                                               ##STR61## Cl    H  H  Cl        S   oil                                  3.16                                                                               ##STR62## OCH.sub.3                                                                           H  H  Cl        S   m.p. 46-49° C.                3.17                                                                               ##STR63## Cl    H  H  OCH.sub.2 CH.sub.2 OCH.sub.3                                                            S   oil                                  3.18                                                                              CHF.sub.2  Cl    H  H  OCH.sub.2 CF.sub.3                                                                      S   oil                                  3.19                                                                              CF.sub.2 CHF.sub.2                                                                       H     H  H  H         S                                        3.20                                                                              CF.sub.2 CHF.sub.2                                                                       Cl    H  Hi Cl        S                                        3.21                                                                              CF.sub.2 CHF.sub.2                                                                       H     H  H  H         O                                        3.22                                                                              CHF.sub.2  n-C.sub.3 H.sub.7                                                                   H  H  Cl        S                                        3,23                                                                              CHF.sub.2  Cl    H  H   NHCH.sub.3                                                                             S                                        3.24                                                                              CHF.sub.2  Cl    H  H  OH        S                                        3.25                                                                              CHF.sub.2  Cl    H  H  NH.sub.2  S                                        3.26                                                                              CHF.sub.2  Cl    H  H  NHC.sub.2 H.sub.5                                                                       S                                        3.27                                                                              CHF.sub.2  Cl    H  H  NHC.sub.3 H.sub.7 (i)                                                                   S                                        3.28                                                                              CHF.sub.2  CH.sub.3                                                                            H  H  CH.sub.3  S                                        3.29                                                                              CHF.sub.2  SCH.sub.3                                                                           H  H  SCH.sub.3 S                                        3.30                                                                              CH.sub.2 CN                                                                              H     H  H  H         S                                        3.31                                                                              CH.sub.2 CN                                                                              H     H  H  H         O                                        3.32                                                                              CBrF.sub.2 H     H  H  H         S                                        3.33                                                                              CBrF.sub.2 H     H  H  H         O                                        3.34                                                                              CH.sub.2 CH.sub.2 CFCF.sub.2                                                             Cl    H  H  Cl        O   oil                                  3.35                                                                              CH.sub.2 CH.sub.2 CFCF.sub.2                                                             H     H  H  H         O   n.sub.D.sup.25 1.5527                3.36                                                                              CHF.sub.2  H     H  H  H         O   m.p. 88-93° C.                __________________________________________________________________________

    ______________________________________                                        2. Formulation Examples for liquid active ingredients of formula I            (throughout, percentages are by weight)                                       2. 1. Emulsifiable concentrates                                                                      (a)    (b)       (c)                                   ______________________________________                                        a compound of Tables 1-3                                                                             25%    40%       50%                                   calcium dodecylbenzenesulfonate                                                                      5%     8%        6%                                    castor oil polyethylene glycol ether                                                                 5%     --        --                                    (36 moles of ethylene oxide)                                                  tributylphenol polyethylene glycol ether                                                             --     12%       4%                                    (30 moles of ethylene oxide)                                                  cyclohexanone          --     15%       20%                                   xylene mixture         65%    25%       20%                                   ______________________________________                                    

Emulsions of any required concentration can be produced from suchconcentrates by dilution with water.

    ______________________________________                                        2.2. Solutions     (a)          (b) (c)  (d)                                  ______________________________________                                        a compound of Tables 1-3                                                                         80%          10% 5%   95%                                  ethylene glycol monomethyl ether                                                                 20%          --  --   --                                   polyethylene glycol (mol. wt. 400)                                                               --           70% --   --                                   N--methyl-2-pyrrolidone                                                                          --           20% --   --                                   epoxidised coconut oil                                                                           --           --  1%   5%                                   petroleum distillate (boiling range                                                              --           --  94%  --                                   160-190° C.)                                                           ______________________________________                                    

These solutions are suitable for application in the form of microdrops.

    ______________________________________                                        2.3. Granulates      (a)           (b)                                        ______________________________________                                        a compound of Tables 1-3                                                                           5%            10%                                        kaolin               94%           --                                         highly dispersed silicic acid                                                                      1%            --                                         attapulgite          --            90%                                        ______________________________________                                    

The active ingredient is dissolved in methylene chloride, the solutionis sprayed onto the carrier, and the solvent is subsequently evaporatedoff in vacuo.

    ______________________________________                                        2.4. Dusts           (a)           (b)                                        ______________________________________                                        a compound of Tables 1-3                                                                           2%            5%                                         highly dispersed silicic acid                                                                      1%            5%                                         talcum               97%           --                                         kaolin               --            90%                                        ______________________________________                                    

Ready-for use dusts are obtained by intimately mixing the carriers withthe active ingredient.

    ______________________________________                                        Formulation Examples for solid active ingredients of formula I                (throughout, percentages are by weight)                                       2.5. Wettable powders                                                                              (a)         (b)     (c)                                  ______________________________________                                        a compound of Tables 1-3                                                                           25%         50%     75%                                  sodium lignosulfonate                                                                              5%          5%      --                                   sodium lauryl sulfate                                                                              3%          --      5%                                   sodium diisobutylnaphthalenesulfonate                                                              --          6%      10%                                  octylphenol polyethylene glycol ether                                                              --          2%      --                                   (7-8 moles of ethylene oxide)                                                 highly dispersed silicic acid                                                                      5%          10%     10%                                  kaolin               62%         27%     --                                   ______________________________________                                    

The active ingredient is thoroughly mixed with the adjuvants and themixture is thoroughly ground in a suitable mill, affording wettablepowders which can be diluted with water to give suspensions of thedesired concentration.

    ______________________________________                                        2.6. Emulsifiable concentrate                                                 ______________________________________                                        a compound of Tables 1-3 10%                                                  octylphenol polyethlene glycol ether                                                                   3%                                                   (4-5 moles of ethylene oxide)                                                 calcium dodecylbenzenesulfonate                                                                        3%                                                   castor oil polyglycol ether                                                                            4%                                                   (35 moles of ethylene oxide)                                                  cyclohexanone            30%                                                  xylene mixture           50%                                                  ______________________________________                                    

Emulsions of any required concentration can be obtained from thisconcentrate by dilution with water.

    ______________________________________                                        2.7. Dusts           (a)           (b)                                        ______________________________________                                        a compound of Tables 1-3                                                                           5%            8%                                         talcum               95%           --                                         kaolin               --            92%                                        ______________________________________                                    

Ready-for-use dusts are obtained by mixing the active ingredient withthe carrier, and grinding the mixture in a suitable mill.

    ______________________________________                                        2.8. Extruder granulate                                                       ______________________________________                                        a compound of Tables 1-3 10%                                                  sodium lignosulfonate    2%                                                   carboxymethylcellulose   1%                                                   kaolin                   87%                                                  ______________________________________                                    

The active ingredient is mixed and ground with the adjuvants, and themixture is subsequently moistened with water. The mixture is extrudedand then dried in a stream of air.

    ______________________________________                                        2.9. Coated granulate                                                         ______________________________________                                        a compound of Tables 1-3  3%                                                  polyethylene glycol (mol. wt. 200)                                                                      3%                                                  kaolin                    94%                                                 ______________________________________                                    

The finely ground active ingredient is uniformly applied, in a mixer, tothe kaolin moistened with polyethlene glycol. Non-dusty coatedgranulates are obtained in this manner.

    ______________________________________                                        2.10. Suspension concentrate                                                  ______________________________________                                        a compound of Tables 1-3  40%                                                 ethylene glycol           10%                                                 nonylphenol polyethylene glycol                                                                         6%                                                  (15 moles of ethylene oxide)                                                  sodium lignosulfonate     10%                                                 carboxymethylcellulose    1%                                                  37% aqueous formaldehyde solution                                                                       0.2%                                                silicone oil in the form of a 75%                                                                       0.8%                                                aqueous emulsion                                                              water                     32%                                                 ______________________________________                                    

The finely ground active ingredient is intimately mixed with theadjuvants, giving a suspension concentrate from which suspensions of anydesired concentration can be obtained by dilution with water.

Biological Example 3.1 Action against Meloidogyne incognita on tomatoplants

Eggs of Meloidogyne incognita are mixed into sand. This mixture is thenput into 200 ml earthenware pots (5000 eggs per pot). On the same day athree-week-old tomato plant is planted in each pot and the formulatedtest compound is introduced into the pots by drench application (0.0006%of active ingredient, based on the volume of the soil). The pottedplants are stood in a greenhouse at a temperature of 26±1° C. and arelative humidity of 60%. After 4 weeks evaluation is made by examiningthe plants for root-knot formation in accordance with the Knot Index.

Compounds of Tables 1 to 3 exhibit good activity against Meloidogyneincognita in that they substantially reduce root-knot formation. On theother hand, untreated and infected control plants exhibit severeroot-knot formation (=100%). Thus, in this test, e.g. compounds 1.1, and2.11 inhibit root-knot formation almost completely (0-10% infestation).

What is claimed is:
 1. A 2-mercapto-5-pyridyl-1,3,4-oxadiazole or2-mercapto-5-pyridyl-1,3,4-thiadiazole of the formula (I) ##STR64##wherein X is oxygen or sulfur,R' is C₁ -C₃ alkyl which is substituted bybromine, fluorine, C₁ -C₃ alkoxy or cyano; unsubstituted orhalogen-substituted C₃ -C₇ alkenyl; halogen-substituted C₄ -C₇ alkynyl,R is C₁ -C₃ alkyl; or halo-C₁ -C₃ alkyl unsubstituted C₁ -C₃ alkoxy orC₁ -C₃ alkoxy which is substituted by halogen or C₁ -C₃ alkoxy;unsubstituted or halogen-substituted C₃ -C₇ alkenyl; C₃ -C₇ alkynyl, C₁-C₃ alkylthio; halogen; cyano; hydroxy, amino or amino which issubstituted by one or two C₁ -C₃ alkyl groups; or is aminocarbonyl; andn is 0, 1, 2, 3 or 4,or a salt thereof.
 2. A 2-mercapto-5-(pyrid-2-yl)1,3,4-oxadiazole according to claim 1 of the formula ##STR65## whereinR' is difluoromethyl, the substituents R₁, R₂ and R₃ are hydrogen and R₄is aminocarbonyl or hydroxy.
 3. A2-mercapto-5-(pyrid-2-yl)-1,3,4-oxadiazole according to claim 1 of theformula ##STR66## wherein R' difluoromethyl or cyanomethyl and R₁, R₂,R₃ and R₄ are hydrogen. 4.2-Difluoromethylthio-5-(pyrid-2-yl)-1,3,4-oxadiazole according toclaim
 1. 5. A 2-mercapto-5-(pyrid-2-yl)thiadiazole according to claim 1of the formula ##STR67## wherein R' is C₁ -C₃ alkyl which is substitutedby bromine, fluorine or cyano; allyl or halogen-substituted allyl; R₁,R₂, R₃ and R₄ are each independently hydrogen, methyl, difluoromethyl,trifluoromethyl, methoxy, methylmercapto, chlorine, cyano, hydroxy,amino or aminocarbonyl.
 6. A compound according to claim 5, wherein R₁and R₂ are each independently of the other hydrogen or chlorine and R₂and R₃ are hydrogen.
 7. A compound according to claim 5, wherein R' isdifluoromethyl, R₁, R₂ and R₃ are hydrogen and R₄ is methyl,trifluoromethyl, methoxy, chlorine, cyano, aminocarbonyl, hydroxy oramino.
 8. A compound according to claim 5, wherein R' is difluoromethyl,one of the substituents R₁, R₂ and R₃ is methyl, chlorine, methoxy ormethylmercapto and the other two substituents are hydrogen and R₄ ishydrogen.
 9. A compound according to claim 5, wherein R' isdifluoromethyl, R₁ and R₄ are each independently of the other hydrogen,chlorine, methoxy or hydroxy, and R₂ and R₃ are hydrogen. 10.2-Difluoromethylthio-5-(pyrid-2-yl)-1,3,4-thiadiazole according to claim9.
 11. A 2-mercapto-5-(pyrid-3-yl)oxadiazole according to claim 1 of theformula ##STR68## wherein R' is difluoromethyl and one of thesubstituents R₁, R₂, R₃ and R₄ is methyl, methylmercapto or halogen andthe other three sustituents are hydrogen.
 12. A2-mercapto-5-(pyrid-3-yl)oxadiazole according to claim 1 of the formula##STR69## wherein R' is difluoromethyl and R₁ and R₄ are eachindependently of the other methyl or chlorine and R₂ and R₃ arehydrogen.
 13. A 2-mercapto-5-(pyrid-3-yl)oxadiazole according to claim 1of the formula ##STR70## wherein R' is difluoromethyl, R₁ and R₄ arechlorine and one of the substituents R₂ and R₃ is hydrogen or chlorine.14. A 2-mercapto-5-(pyrid-3-yl)oxadiazole according to claim 1 of theformula ##STR71## wherein R' is difluoromethyl and R₁, R₂, R₃ and R₄ arehydrogen.
 15. A 2-mercapto-5-(pyrid-3-yl)thiadiazole according to claim1 of the formula ##STR72## wherein R' is difluoromethyl ordifluoromethyldifluoromethyl and R₁, R₂, R₃ and R₄ are hydrogen.
 16. A2-mercapto-5-(pyrid-3-yl)-thiadiazole according to claim 1 of theformula ##STR73## wherein R' is difluoromethyl, R₁ is hydrogen, C₁ -C₃alkyl or chlorine, R₂ is hydrogen and R₃ and R₄ are each independentlyof the other hydrogen or chlorine or methoxy.
 17. A2-mercapto-5-(pyrid-3-yl)thiadiazole of the formula ##STR74## accordingto claim 16, wherein R' is difluoromethyl, R₁, R₂ and R₄ are eachindependently hydrogen, chlorine, bromine, methylthio or amino, and R₃is hydrogen.
 18. 2-Difluoromethylthio-5-(pyrid-3-yl)-1,2,4-thiadiazoleaccording to claim
 17. 19. A 2-mercapto-5(pyrid-4-yl)-oxadiazoleaccording to claim 1 of the formula ##STR75## wherein R' isdifluoromethyl, difluoromethyldifluoromethyl or cyanomethyl, and R₁, R₂,R₃ and R₄ are hydrogen.
 20. A 2-mercapto-5-(pyrid-4-yl)-thiadiazoleaccording to claim 1 of the formula ##STR76## wherein R₂ and R₃ arehydrogen.
 21. A compound according to claim 20, wherein R' isdifluoromethyl, difluoromethyldifluoromethyl, cyanomethyl or2-bromoallyl, R₁ is hydrogen, C₁ -C₄ alkyl, chlorine, methoxy ormethylmercapto, R₄ is hydrogen, methyl, chlorine, methoxyethoxy,trifluoromethylmethoxy, methylmercapto, amino or C₁ -C₃ monoalkylamino.22. Difluoromethylthio-5-(pyrid-4-yl)-1,3,4-thiadiazole according toclaim
 21. 23. A pesticidal composition for controlling nematodes or forprotecting plants from attack by nematodes, which composition containsas active component a pesticidally active amount of at least onecompound of claim
 1. 24. A method of controlling nematodes or ofprotecting cultivated plants from attack by nematodes, which methodcomprises applying to the plant or to the locus thereof a compound ofthe formula ##STR77## wherein X is oxygen or sulfurR is hydrogen, C₁ -C₃alkyl, C₁ -C₃ alkoxy which is substituted by halogen or C₁ -C₃ alkoxy;C₃ -C₇ alkenyl or halogen-substituted C₃ -C₇ alkenyl; C₃ -C₇ alkynyl; C₁-C₃ alkylthio; cyano, halogen, hydroxy; amino or amino which issubstituted by one or two C₁ -C₃ alkyl groups; or is aminocarbonyl, R'is C₁ -C₃ alkyl which is substituted by halogen, C₁ -C₃ alkoxy or cyano;C₃ -C₇ alkenyl or halogen-substituted C₃ -C₇ alkenyl; unsubstituted orsubstituted C₃ -C₇ alkynyl; and n is 0, 1, 2, 3 or 4.